Preheat the oven to 350°F. Butter a 9-x-13-inch baking pan and set aside. Combine the butter and 1½ cups of the chocolate in a large microwave-safe bowl and microwave until smooth; 1½ to 2 minutes; cool for 5 minutes.

Whisk in the sugar, then the vanilla, espresso, salt, and eggs until smooth. Combine the flour, cocoa, and baking powder in a small bowl, then whisk into the batter until smooth.

Stir in the pecans and the remaining ½ cup chocolate chips until just combined. Transfer the batter to the buttered baking pan, smooth the top to even it out, and bake until the brownies have hardened on the top and are just set, 22 to 24 minutes. Remove from the oven, cool completely, and dust with confectioners sugar. Cut into 16 squares.